1. Field of the Invention
The present invention relates to a delay circuit, more particularly, to a delay circuit manufacturable by semiconductor elements and used for digital signal processing and analog signal processing.
In analog circuits, a delay circuit is used for processing various signals, for example, as a ghost canceller in a television signal circuit, or as a pulse shaper in a hard disk. On the other hand, in digital circuits, a delay circuit is used for regulating signal timings. For example, a digital filter is in a category of such a delay circuit. A digital filter generally includes a plurality of delay circuits each having a constant time lag and connected in a cascade connection, where predetermined weights are added to respective signals at the connection points between the delay circuits and thus addition and subtraction of the weighted signals are carried out. Thus, delay circuits are widely utilized in various applications.
2. Description of the Related Art
Delay circuits are generally constituted using passive elements such as capacitors, inductance components and the like, or using active elements such as transistors and the like.
With respect to delay circuits using passive elements, however, there are posed a number of problems. For example, where the delay circuit is connected by multiple stages, the attenuation factor of the delayed signal becomes large due to resistance components occurring in series with inductance components. Also, since respective values of the inductance components and the capacitors are constant, it is difficult to easily change the delay time. Furthermore, since the inductance components cannot be manufactured by semiconductor elements, it is impossible to realize a small size, high performance and low cost of the delay circuit.
On the other hand, delay circuits using active elements pose a problem in that, where a relatively long delay time is obtained, the frequency band of the delayed output signal becomes narrow.
Note, the problems in the prior art will be explained later in detail in contrast with the preferred embodiments of the present invention.